staff hold needle caps in their mouth while they were giving an injection, and i thought that there was a potential there for saliva dna. >> i thought that was rather brilliant, in fact. >> dna analysts swabbed the needle caps and found biological material. >> on the needle cap or cover, there was an unknown male dna profile. >> and scientists also found dna inside the syringe. >> i was able to determine that miss herndon's dna was present in one of them. >> proof it had been used on michelle. michelle's death was now classified as a homicide. and the murder weapon was propofol. >> i've never seen a propofol-related death. ever. >> but who wanted michelle dead? (vo) around age 7, the glucose metabolism in a dog's brain begins to change. (maryjo) she's always interacted